(A) Field of the Invention
The present invention is related to an LED (light emitting diode) apparatus, more specifically, to an LED apparatus having temperature control functions.
(B) Description of the Related Art
In recent years, white light LED is an attractive new product with increasing importance around the world. It has the advantages of small volume, low power consumption, long lifetime and quick response, and can solve many problems that exist with an incandescent lamp.
In view of the consensus of Japan, European countries, and the U.S. on power saving and environmental protection, the countries are actively developing white light LED as the luminance source for this century. In addition, if all incandescent lamps are replaced with white light LEDs, electric power consumption can be diminished and carbon dioxide (CO2) generation can be decreased so as to reduce the greenhouse effect. Accordingly, European countries, the U.S. and Japan are investing manpower on R&D, and white light LED is predicted to replace conventional lamp technology within ten years.
Current LED apparatus for luminance may integrate plural LEDs as an illuminant module, or use so-called large chip process. However, regardless of the arrangement in use, the tiny LED package has to effectively dissipate high heat, otherwise product reliability issues may arise due to the different expansion coefficients of the LED package materials, and the illuminant efficiency will significantly decrease as the temperature goes up. The LED apparatus' lifetime is reduced by high temperatures as well. Therefore, ability to avoid destructive high heat while illuminating becomes important for LED applications.
It is obvious that LED apparatus should incorporate a design for heat dissipation. One design solution is to use a metal leadframe below the LED chip to dissipate the heat generated from the LED. However, in order to improve the brightness, a high efficiency LED using a light source consisting of plural LEDs or large chip still suffers poor heat dissipation efficiency. Another design solution is to use temperature or current control IC to control the input current to LED. However, not only the IC solution is an expensive solution, but also the IC itself generates heat and has heat dissipation problem. The IC solution needs additional heat dissipation mechanism to achieve a better heat management for LED. It is most desirable that a self-regulating and temperature sensing device, such as PTC, should be incorporated into the IC controlled LED system.